Loco wheels cast iron grade ?

[Former MemberParticipant @formermember19781]

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[Former MemberParticipant @formermember19781]

[Former MemberParticipant @formermember19781]

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[Ron LadenParticipant @ronladen17547]

Hi Bill,

I was reading up on cast iron a while back and remember someone saying that SG iron was stronger and better for wheels than 250 but that is only what I read I dont have any knowledge of it myself.

The plain disc wheels on my electrics are in EN8 steel but I bought them in so I guess that is not based on which is best but more a cost and convenience in production thing.

Sorry, not very helpful but hopefully someone more knowledgeable will be along shortly.

Ron

[Former MemberParticipant @formermember19781]

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[Ron LadenParticipant @ronladen17547]

Bill,

17D Miniatures is where I purchased my wheels, they have a website. The only thing is most of what they produce and stock is 5" and 7 1/4". They do offer a machining service though and wheels is one of the products they list but how it works price wise when its not a stock item I dont know. It would certainly be worth giving them a ring as I have found them really helpful.

Tel: 01629 825070 Mon – Friday 9.30 – 5.00. Also the website has an enquiry form you can send them.

Ron

 

Edited By Ron Laden on 09/09/2019 18:51:40

[Anonymous]

Cast iron is strong in compression but relatively weak in tension. And it is not ductile, so wouldn't stand up to the hammering from the track and out of balance forces. In contract SG iron is processed so that it is good in tension and compression. As examples both the front axles and crankshafts on my traction engines are SG iron castings. It's a PITA to machine as it chatters more than an Islington lovie. Cue a response from Jason saying it's no problem. However, for disc wheels steel will be even better, probably cheaper and less messy to machine.

Full size spoked wheels consisted of a cast iron centre with a shrunk on steel tire. The steel tire had good wear and shock load capabilities and being shrunk on put the cast iron centre in compression.

Andrew

[old martParticipant @oldmart]

My only experience of machining ductile iron (SG) is in modifying lathe chucks, and I found it so much better to machine than mucky, dusty regular CI.

[Former MemberParticipant @formermember19781]

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[JasonBModerator @jasonb]

It is certainly not as easy to machien as a free cutting steel or grey cast iron but I do think some of teh chatter problems also come from the crankshaft shape.

This one I roughed out the two main lengths before doing the pin.

Here you can see the chatter on them but teh pin which has been finished is better

Once the throws at the ends can be removed a lot of the chatter can be reduced buy effectively shortening the length buy sticking half of it up the spindle which allows a decent finish.

This one turned out OK too.

The Americans seem to use it more for some of the smaller castings on their engine kits rather than the gun metal that gets used over here and I have not noticed chatter on them so this goes some way to pointing to the length and shape of the crankshafts being part of the problem

[Ron LadenParticipant @ronladen17547]

There is a good number of keyways on that last one Jason, is that off a traction engine.

[JasonBModerator @jasonb]

Yes, the 2" Fowler. It's about 9" long. Keyways from left to right

Flywheel

Slow Pinion

Fast Pinion

Valve eccentrics

Pump Excentric

Unused

[Ron LadenParticipant @ronladen17547]

Very nice Jason, some quality engineering there I fancy.

[Ron LadenParticipant @ronladen17547]

Posted by 34046 on 09/09/2019 20:07:12:

Ron – many thanks

Steel ones from 17D is the answer for me .

Thanks for the contact details.

Bill

Your welcome Bill, but as I mentioned they dont list 3.5 inch gauge as stock so you will have to see what they say.

Ron

[Anonymous]

Wot, no splines?

Both my crankshaft and front axle are long 'n' thin. So definitely a candidate for chatter. But when it happened it proved difficult to get rid of. Eventually cured it by forcing a block wood against the work piece to add damping. It also explains why the diameter of the eccentric side of my crankshaft is different on the two crankshafts.

Andrew

[duncan webster 1Participant @duncanwebster1]

Posted by Andrew Johnston on 09/09/2019 19:25:51:

Cast iron is strong in compression but relatively weak in tension. And it is not ductile, so wouldn't stand up to the hammering from the track and out of balance forces. In contract SG iron is processed so that it is good in tension and compression……..

Full size spoked wheels consisted of a cast iron centre with a shrunk on steel tire. The steel tire had good wear and shock load capabilities and being shrunk on put the cast iron centre in compression.

Andrew

There are hundreds if not thousands of model locos out there with ordinary grey cast iron wheels.

[JasonBModerator @jasonb]

I doubt many of those cast wheels are from such good iron as a bit of 250 bar, do you know what grades the suppliers use? I suspect it is harder.

Andrew, you don't get splines on a 4 shaft engines crankshaft, at least not this one as they are on the 2nd shaft.

Yes needs a good sharp HSS or **GT insert anf small DOC to get rid of the chatter as a normal insert tends to deflect the long shafts more unless you are able to resort to a cylindrical grinder.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 09/09/2019 19:25:51:

Cast iron is strong in compression but relatively weak in tension. And it is not ductile, so wouldn't stand up to the hammering from the track and out of balance forces.

[ … ]

.

Not my specialist subject at all, Andrew … So please explain gently:

What, then, does the word ductile mean in relation to the thousands [probably millions] of iron grids and covers in our roadways etc. ?

I can only assume that 'ductile' is a relative term rather than a binary one.

MichaelG.

.

Edit: … a brief self-help exercise found this:

https://willmanind.com/what-ductile-iron/

Edited By Michael Gilligan on 10/09/2019 07:30:17

[JasonBModerator @jasonb]

"cast iron" as used by Andrew in his reply can be taken as referring to grey cast iron

The ductile irons are like Andrew goes on to mentioned such as  SG iron where the iron structure is different so they are less brittle and more ductile

Have a look at 500/7 iron for your manholes as opposed to the usual 250 bar that most on here refer to when talking of cast iron bar. Our crankshaft castings are more likely from 700 grade which is even more ductile. Numbers tend to denote tensile strength.

 

Edited By JasonB on 10/09/2019 08:34:18

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 10/09/2019 08:14:26:

"cast iron" as used by Andrew in his reply can be taken as referring to grey cast iron

[ … ]

.

 So … "cast iron" is another Model Engineering jargon term [?]

I think I'm happy with Willman's explanation.

MichaelG.

Edited By Michael Gilligan on 10/09/2019 08:54:31

[Anonymous]

Posted by JasonB on 10/09/2019 07:12:55:

………….unless you are able to resort to a cylindrical grinder.

That would have been the preferred option, but my cylindrical grinder is only 12" between centres.

Andrew

[GordonHParticipant @gordonh]

Posted by Michael Gilligan on 10/09/2019 07:25:41

What, then, does the word ductile mean in relation to the thousands [probably millions] of iron grids and covers in our roadways etc. ?

Michael,

When a heavy load passes over a grid or a cover, bending occurs about the neutral axis. In the case of a grid, the underside of the bars is in tension, for a cover, the tensile load is in the underside of the webs. In both cases, the SG iron's superior tensile strength leads to another of its superior properties, improved fatigue strength. Without this, fatigue failure would eventually occur.

Jason was quicker typing than me.

Gordon

[SillyOldDufferModerator @sillyoldduffer]

My understanding is the advantage of cast-iron wheels is complex forms can be made in a mould and then simply finished to size, a major time-saver. Apart from that cast-iron isn't ideal as a material for making wheels for the reasons Andrew listed. I'd also add cast-iron's well-known lubricating properties – good enough for a cheap bearing – which is likely to reduce its grip on a rail. Full size wheels are fitted with steel tyres.

Given a choice of making wheels from bar stock, I'd go for steel rather than cast-iron. I can't think of a good reason to fabricate wheels from cast-iron even in the most suitable grade. Aside from anything else it's filthy stuff to machine.

Part of the fun to be had in a workshop is learning what matters and what doesn't! Engineering books don't always help. Although there are occasions where materials have to be 'just so', for many amateur purposes whatever is most convenient can often be used. It's because the stresses and strains imposed on a model are likely to be less critical than on full-size, where for example, it can be vital to trade-off strength and weight to achieve high fuel-efficiency.

As Stewart Hart's PottyMill is far more forgiving than a performance model aircraft IC engine the trick is learning the art of compromise. I can confirm ill-educated bodging and slavishly trying to imitate engineering best-practice both lead to disappointment! For me the forum has proved to be an excellent source of practical advice.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Gordon

Yes … as I said to Jason, I have read and understood Willman's explanation.

What surprises me is that in a thread about grades of cast iron … a casual generalisation is being used.

… rather like the routine abuse of the words 'Loctite' and 'Aluminium'

I thought that Andrew would be above such things, and therefore asked him a direct question.

MichaelG.

[Anonymous]

Who'd have thought so little could generate so much! Must remember to attach a detailed glossary to future posts.

Andrew

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